Ulster was commissioned in the King's Royal Hussars on 10 April 1998 as a subaltern (second lieutenant) with seniority from 14 April 1995; he was given the service number 548299. He was promoted to lieutenant on 10 April 1998 with seniority from 14 April 1997,[2] and to the rank of captain on 16 October 2000.[3] He saw active service in Northern Ireland, Kosovo in 2002, as well as Iraq. He served in the MND(SE) as an Information Operations staff officer. In Basrah he was responsible for advising on divisional level KLE, monitoring atmospherics within the city and advising on the communications strategy pertinent to the handover of Basrah Palace.[1] On 14 January 2003, he transferred from a Short Service Commission to an Intermediate Regular Commission.[4] On 28 April 2008, he was appointed to the Reserve of Officers, signalling his retirement from the British Army with the rank of actingmajor.[5]

Since leaving military service, Ulster has worked as director of Transnational Crisis Project.

Claire Alexandra Windsor, Countess of Ulster (born Claire Alexandra Booth on 29 December 1977) is the wife of Alexander Windsor, Earl of Ulster. A physician by profession, she prefers to remain known as Dr Claire Booth.